It is well-known to prepare erythritol by fermentation using microorganisms. The microorganisms so far known to be capable of producing erythritol include, for instance, those belonging to Aureobasidium sp. (Japanese Patent Laid-Open Publication No. 61-31091), Moniliella sp. (EP Publication No. 0,136,805), Candida zeylanoides (Japanese Patent Laid-Open Publication No. 49-118889), Candida lipolytica (U.S. Pat. No. 3,756,917), Debaryomyces sp. (U.S. Pat. No. 2,986,495), Pichia sp. (U.S. Pat. No. 2,986,495), Moniliella sp. (Antonie van Leeuwenhoek, 37, 107-118 (1971) and Applied Microbiology, 12(3), 240-246 (1964)), and the like.
However, such known microorganisms have not still been used on an industrial scale due to their grave disadvantages that cannot practically be neglected.
More exactly, Japanese Patent Laid-Open Publication No. 61-31091 and EP Publication No. 0,136,805 describe methods for preparing erythritol from monosaccharides with the use of Aureobasidium sp. and Moniliella sp. microorganisms, respectively. These methods make it possible to prepare erythritol using a relatively high substrate concentration of a culture media and, hence, are valuable in their own ways. However, these methods are not always satisfactory owing to the disadvantages that a large amount of antifoamer should be added since marked foaming occurs at the time of culture. Furthermore, Japanese Patent Laid-Open Publication No. 61-31091 is disadvantageous in that the yield of erythritol are not only unsatisfactory relative to the amount of cells grown by microorganisms, but the optimum pH, temperature and the like are also narrow, and, even if such factors depart slightly from the optimum ranges, there is then a remarkable drop of the yield of erythritol.
U.S. Pat. No. 2,986,495 discloses a method for preparing arabitol, glycerol and erythritol from monosaccharides with the use of Pichia sp. and Debaryomyces sp. microorganisms. According to this method, however, while glycerol and arabitol would be produced as the major product, only a small amount of erythritol may be produced as the byproduct, which should be separated out and collected with considerable difficulty.
U.S. Pat. No. 3,756,917 teaches a method for the preparation of erythritol from hydrocarbons using Candida sp. microorganisms. However, this method is of low productivity and so uneconomical due to the need that the substrate concentration be at most 20%. Another potential disadvantage is the possibility that the starting hydrocarbons may remain in the product.
Antonie van Leeuwenhoek, 37, 107-118 (1971) and Applied Microbiology, 12(3), 240-246 (1964) describes a method for preparing erythritol from glucose with the use of Moniliella (Torula) sp. microorganisms. This method is characterized in that the ratio of conversion of glucose to erythritol is high and the substrate concentration of a culture media may be increased to a relative high level, but has the disadvantage that a large amount of xanthane gum should be used for defoaming, since marked foaming occurs at the time of culture.
It has been found by the present inventors that erythritol can be produced by Trichosporonoides madida isolated from a honeycomb. However, the ability of this wild T. madida to produce erythritol was not high enough for industrial use.
A novel high erythritol producing strain T. madida KCTC 8712P having high osmotic tolerance was developed by the present inventors. This strain was prepared by treating the above wild-type erythritol producing T. madida with a mutagenic agent N-methyl-N'-nitro-N-nitrosoguanidine. However, a method of producing erythritol using T. madida KCTC 8712P strain are not practical since lots of foaming occur during culture and thus reduce the efficiency of the fermentor.
In view of the fact that reducing aeration rate makes it possible to decrease the foams occurred during culture, the present inventors strived to develop T. madida strains requiring a less oxygen supply while maintaining the high erythritol productivity.